Mechanically tuned magnetrons are widely available, but they suffer from two distinct disadvantages. This type of magnetron can provide only slow frequency tuning, and requires that moving parts penetrate the vacuum envelope of the magnetron, which has an impact on the reliability of the device.
Mechanically tuned magnetron oscillators are typically one of two types, the plunger-tuned magnetron and the coaxial magnetron. The plunger-tuned magnetron uses a plunger to which metallic probes are attached, and inserts and retracts probes from each of the magnetron's resonant cavities in order to perturb their resonant frequencies. FIG. 1 illustrates an exemplary plunger-tuned magnetron, using a "crown-of-thorns" tuning scheme, in cross-section. The anode block encircles the cathode, and a number of resonant cavities are formed in the end spaces between the anode block and the cathode. The inductive tuning elements, supported on a tuner frame, are inserted into and retracted from the resonant cavities on bellows, in order to change the cavities' inductance and hence their resonant frequencies.
The coaxial magnetron places the magnetron anode block inside a coaxial resonant cavity, whose dimensions are mechanically changed to tune the frequency.
Both types of magnetrons suffer from all the disadvantages inherent in mechanically tuned mechanisms, i.e., they are slow and require that moving parts penetrate the vacuum envelope.
It would therefore represent an advance in the art to provide an electronic tuning mechanism for a magnetron oscillator so that the frequency can be varied more rapidly than is possible with mechanical tuning.
It would further be advantageous to provide a magnetron oscillator wherein device construction is simplified with no moving parts penetrating the vacuum envelope, thereby lowering the fabrication cost and providing increased reliability.